The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
Transfer cases are used in all-wheel drive vehicles for the splitting of the torque to a plurality of axles, in particular to the front axle and the rear axle. This is possible in different modes, for instance with a longitudinal differential lockable by a multiple disk clutch. A further mode includes the engagement of the connection to the secondary shaft which is usually associated with the front axle. On engagement by means of a controllable friction clutch, one speaks of “torque on demand”.
The lubrication of transfer cases with their large height differences due to the offset drive and with the high cooling oil requirement of the friction clutch, above all in slip operation, usually requires a separate oil pump which is driven by the primary shaft and which has to be configured to the maximum lubricating oil demand with a slipping clutch due to the non-controllable drive. The power loss in the transfer case caused by the oil pump is thereby substantial.
A transfer case having a longitudinal differential and a multiple disk clutch is known from EP 268 904 in which oil should move from an annular space surrounding the primary shaft up to the clutch disposed far away while dispensing with an oil pump. A rotating collar is provided for this purpose whose cylindrical part has inwardly screw-shaped oil conveying beads. The annular space between the primary shaft and a hollow shaft which surrounds it and is part of the offset drive is long and narrow so that a sufficient and reliable oil supply is doubtful, in particular when the friction clutch is operated with slip for a longer time.